1. Field of the Invention.
The present invention relates to handheld optical scanners for reading bar code symbols, and more particularly, to a data transmitting format that enables cordless operation for such optical scanners.
2. Description of Related Art
Optical imaging systems are commonly used to decipher data symbology printed on objects in order to identify the objects. A bar code symbol represents a popular form of symbology, and typically comprises a pattern of parallel bars of various widths separated by spaces of various widths. Since the bar and space elements have different light reflecting characteristics, a scanner can convert the bar code symbol into an electrical signal by analyzing the light reflected from the symbol. The electrical signal can then be decoded to provide an alphanumeric representation of the symbol which identifies the object. Bar code symbols of this nature are commonly used in inventory control, point of sale identification, transportation, or other such material handling applications.
The typical bar code scanner uses light that is drawn across the bar code field. Since the bar code symbols are often disposed on the object to be identified, it is desirable for the scanner to be included in a handheld or portable device so that the scanner can be brought to the object. Light emitting diodes (LEDs) are commonly utilized within such scanners to provide the scanning light due to their light weight and low power requirements. The operator can physically move the LED across the bar code field, such as by use of a light pen or wand. Alternatively, a bar code scanner may include movable mirrors that automatically articulate the light back and forth at a high rate to scan across the bar code field. The operator would normally be provided with a feedback signal, such as an audible tone, that notifies the operator of the successful completion of a bar code reading operation.
Conventional light pens are tethered or connected to a base processor by a cable. These light pens usually include little more than a light emitting element such as the LED, a light detecting element for receiving the reflected light, an associated amplifier, and an analog to digital (A/D) converter. The light detecting element may comprise a conventional photo-diode, photo-transistor, or charge coupled device (CCD) type sensor. The reflected light is detected by the light detecting element, which produces an electrical signal that represents the reflected light. The electrical signal is then amplified by the amplifier and converted to a digital output signal by the A/D converter. The cable carries electrical power from the base processor to the light pen, and carries the digital output signal to the base processor. By virtue of its relative unsophistication, a light pen can be small, lightweight and inexpensive. The circuitry necessary to decode the alphanumeric data from the digital output is contained within the base processor, which may further communicate with another centralized processor.
A drawback of tethered light pens is that the cable can often be cumbersome for the operator to use. For example, the cable may not be long enough to reach a bulky item to be scanned, or may get bound up while trying to reach an awkwardly positioned item. To address this problem, cordless handheld scanners have been developed that incorporate radio frequency (RF) technology. These cordless RF scanners are more sophisticated than conventional light pens, and in addition to the elements of a conventional light pen also include decoding circuitry, a power source (e.g., battery pack), and an RF transmitter. The digital output signal is decoded by the decoding circuitry contained within the cordless RF scanner. The decoded data may be stored temporarily in a memory before being transmitted to the centralized base processor over an RF link. The centralized base processor may be capable of receiving inputs from one or more of the cordless RF scanners, providing the scanner operators with substantially greater flexibility and autonomy. These benefits are particularly desirable for certain high volume bar code users that may simultaneously employ numerous scanner operators, such as within a factory environment.
Notwithstanding these significant benefits, however, the cordless RF scanners are necessarily larger and heavier due primarily to the battery pack, and are also more expensive than the relatively simple tethered light pens due to their increased complexity. Moreover, these cordless RF scanners have a relatively high demand for electrical power, requiring frequent battery pack changes and/or recharging cycles. While larger capacity battery packs can increase the usable life of the cordless RF scanners, this also tends to further increase the weight and bulk of the scanners. These drawbacks tend to diminish the desirability of cordless scanners, especially for less intensive bar code users that may only require a single scanner operator.
Accordingly, a critical need exists for a simple, cordless bar code scanner that can communicate with a base processor over an RF link. Ideally, the cordless scanner should have minimal processing capability so as to reduce power consumption and battery capacity, yet be capable of providing a user with the same high level of flexibility, autonomy and convenience typical of more complex, cordless RF scanners.